Lithography is usually reserved for high quality printing, such as advertising, books, publications, and packaging. Lithographic inks are divided basically into two types; so-called heat-set and quick-set.
Lithographic ink users consider that suitable resins and components for heat-set inks and quick-set inks should have the listed qualities:
(1) Magie Oil solvent (aliphatic hydrocarbon) solubility PA1 (2) Fast-drying without excessive energy input PA1 (3) Compatibility with resinous ink vehicles PA1 (4) Low odor PA1 (5) Pigment dispersing and wetting capability PA1 (6) Good transfer properties PA1 (7) Stability on the press (antiskinning and viscosity stability) PA1 (8) Water immisciblity PA1 (9) Gloss PA1 (10) Low tendency to attack rubber printing rolls and blankets PA1 (11) Resistance to rubbing. PA1 --R.sup.2 is an aliphatic radical, preferably linear hydrocarbyl, having 11-23 carbon atoms and containing at least one olefinic double bond, or mixtures thereof, --R.sup.2 being free of terminal double bonds, and PA1 --X-- is either --OR.sup.3 O-- in which R.sup.3 is an aliphatic or cycloaliphatic hydrocarbon residue containing from 2 to 10 carbon atoms, or --O(CH.sub.2 CHR.sup.4 O).sub.n -- where R.sup.4 is --H or --CH.sub.3 and n is an integer from 2-10, or mixtures thereof.
Lithographic inks of commerce are high viscosity paste inks comprised mainly of colored pigment, binder resin, or resinous vehicle and solvent, usually high boiling aliphatic petroleum cuts known as "ink oils." Solvent content is from about 30% to 50% by weight. Minor additives include natural and synthetic waxes, metal salt driers, antioxidants, antiskinning agents, "sweetening" stronger solvents such as tridecyl alcohol (U.S. Pat. No. 3,257,344), and gelling or bodying agents such as aluminum ortho esters (U.S. Pat. No. 3,531,302). The resins are usually high melting (&gt;60.degree. C.) so as to yield hard, non-offsetting, block-resistant and rub-resistant films. Suitable resins are hydrocarbon polymers, rosin derivatives, alkyds, acrylics, styrene-acrylics, and other conventional binders.
"Quick-set" lithographic inks frequently use the higher boiling of the ink oils, such as Magie Oil 535 as solvent and dry at ambient temperature by a combination of evaporation, wicking into paper, and precipitation via design for marginal resin compatibility. "Heat-set" types use lower boiling solvent such as Magie Oil 470 to achieve faster setting, and are dried at very high speeds in ovens, usually gas fired. These "oils" consist essentially of aliphatic hydrocarbons and are described below.
In the heat-set area especially, the printing industry is under increasing regulatory agency pressure to drastically reduce polluting solvent emission. Ink solvent emission is particularly noxious because the high boiling point ink oil solvents required for long term viscosity stability on the press yield dense smoke plumes from the stacks.
U.S. Pat. Nos. 3,766,110 and 3,776,867 disclose solvent-free printing inks based on acid catalyzed urea or melamine formaldehyde resins with hydroxyl functionality. They are certainly free of solvent emission but do emit noxious and toxic formaldehyde on cure. Moreover, it is well known that such systems have limited shelf life, especially with the strong acid catalysts required for acceptably low cure temperatures.
The reactive diluents useful in the present invention are known compounds. For example, U.S. Pat. No. 3,284,385 (Nov. 8, 1966) to G. F. D'Alelio (assigned to Dal Mon Research Corp.), discloses the preparation and anionic polymerization of methacryloxyethyl linoleate, acryloxyethyl linoleate, and drying oil fatty acid analogs. Also, U.S. Pat. No. 2,160,532 (May 30, 1939) to Barrett and Strain (assigned to duPont) relates to the preparation of monomeric mixed esters of polyhydric alcohols such as diols, glycols, etc., with methacrylic acid and drying oil acids. Specifically disclosed are soybean oil diglyceride monomethacrylate, soybean oil monoglyceride dimethacrylate, glycol laurate methacrylate (lauryl alcohol is a saturated alcohol), and related materials. These are used in coatings with peroxide initiators or metal salt driers or with other resins. U.S. Pat. No. 2,593,444 (Apr. 22, 1952) to Harrison (assigned to General Mills), shows esters of acrylic or methacrylic acid and alcohols derived from drying oils. The use of heat settable inks containing drying oil functionality is also known. See for example Chem. Abstr. 82, 141786R.